Electric furnace.



No. 806,173. PATENTED DEC. 5, 1905.

R; W. MYERS. ELECTRIC FURNACE.

UNITED STATES PATENT orr on.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Dec. 5, 1905.

Application filed February 14, 1905. Serial No- 245,595.

To alt whom, it may concern.-

Be it known that I, ROMAINE WV. MYERS, a citizen of the United States, and a resident of the town of Fruitvale, county of Alameda, State of California, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification.

My invention relates to the art of electric heating and applies two physical facts-first, that certain substances, non-conductors at low temperatures, become conductors at high temperatures, and, second, that the heat generated by the passage of an electric current through conductors varies inversely as the radius of said conductors, being an inverse function of said radius in a degree higher than linear, even reaching the square or cube thereof. I am aware that the former of these facts has been applied in electrical constructions to both electric-heating and electriclighting devices and that the latter has been applied in electric lighting as, for instance, in the distribution of electric lights by means of glow-lamps; but the two facts combined have never heretofore to my knowledge been consciously expressed in electrical constructions of any kind. By applying them to electric heaters, as hereinafter described, I attain the effect of increased economy of operation and increased facility of manipulation, which are features especially desirable in dental, chemical, and assaying furnaces, for which purposes my invention is particularly applicable.

My invention may be expressed in various modifications of the construction herein described; but I do not deem it necessary to describe more than one useful means for carrying it into operation.

The primary object of my invention is the production of an electric furnace of econom ical operation and facile manipulation in which temperatures lying between 600 Fahrenheit and the temperature of the electric arc may be produced and controlled.

A secondary object of my invention is to provide an electric heater of economical operation and facile manipulation in which temperatures lying between 600 Fahrenheit and the temperature of the electric arc may be produced and controlled by a device that is capable of withstanding great variations in line voltage, as this cannot be done by finewire heating apparatus.

A third object of my invention is to provide an electric furnace economical in operation and capable of being manipulated with facility, in which temperatures lying between 600 Fahrenheit and the temperature of the electric arc may be produced and controlled bymeans of heating elements which may be heated by potential gradients within the capacity of ordinary commercial lighting circuits, as from one hundred and ten to two hundred and fifty volts, and at the same time be capable of withstanding great variations in the line voltage.

Referring to the drawings herewith, Figure 1 is a longitudinal section of my electric furnace; and Fig. 2 is a cross-section thereof along the line it m, Fig. 1.

Similar letters refer to similar parts in both the views.

The heating element of my furnace consists of the bar or bars a, composed of refractory oxids, silicates, &c., which material is of comparatively high resistance at ordinary temperatures, but becomes conducting when heated. To attain my objects, the aforesaid material is formed into bars or rods and the heatingcurrent transmitted lengthwise therethrough. Such rods or bars may be of any cross-section square, round, or polygonal. They are attached at the ends to terminal rodsb, of grapl ite, high-fusing metal, or other suitable substances. By the use of the rod-shaped heating elements I attain my objects of transmitting the current through conductors of small radius, whereby a high temperature may be produced with economical expenditure of energy and of providing a furnace which may be heated by potential gradients within the capacity of ordinary commercial lighting-circuits, since my rods may be of any length suitable to such capacity and connected in parallel with one another to provide the quantity of heat required. The material of which the rods is composed withstands extreme variations of line voltage. The said materials have been grouped under the name of pyroelectrolytes, and Ishall so designate them in this specification.

The supports for rods (0 consist of blocks or rods 0, of graphite, high-fusing metal, or other suitable substance, in which are cut slots slightly larger than the terminal rods 7), the ends of said rods being inserted in said slots in order to insure a free movement of said rods to allow for expansion and contraction, due to heating and cooling.

Attention is particularly called to the advantage of supportingbars 0 in the before described manner, as it enables the operator to remove an old bar and insert a new one with ease.

The conductivity of bars a increases so rapidly with the rise of temperature that the fusing-point is soon reached. To prevent fusing, I use an exterior resistance (Z, connected in circuit with rods (6, (Z being composed of metal which increases in resistance as its temperature increases, thereby tending to compensate for the decreasing resistance due to the heating of a, or resistance (Z may be a wire of large diameter and of length sufficient to prevent the fusing of a by its natural cold resistance. into parts, said parts being connected to contact-points, whereby through a sliding contact-piece its resistance may be varied at will, may be used. Thus the current is regulated, and any desired heat corresponding to the amount of energy used in heating the bars a may be maintained.

The inner walls 7' of my furnace are composed of fire-clay or other suitable fire-resisting material. The outer wall is composed of asbestos.

The material to be acted on by my furnace is inserted in the space-inclosing bars a. In order to facilitate its withdrawal and insertion, I provide bars m, of graphite, high-fusing metal, or other suitable material, placed near and parallel to the bars a to prevent the material to be fused or heated from coming into contact with bars a.

The resistances d and lb, described and illustrated herein, are a ready means of varying the electromotive force applied to bars a; but I do not confine myself to the use of resistances for the purpose, as the same result may be obtained with counter electromotive forces or transformers without departing from my invention.

Bars 60 being practically non-conducting when cold, in order to cause current to flow through them it is necessary to subject them to an initial heating. This heating may be effected by means of a blowpipe or other similar source of intense heat. Vhere more than one rod a is used, it will only be necessary to initially heat one of them, the others receiving the necessary heat from this one after it is put in operation.

A second resistance It, divided The circuits through the bars a are connected in parallel, as shown through f, it, upper (Z, left-hand a, g, and e, and through lower (Z, right-hand a, and 0.

My invention is particularly adapted for the fusing of metals, porcelain, &c., for dental, chemical, assaying, or purposes where a relatively low or extremely high temperature is to be produced and uniformly maintained.

I claim 1. An electric furnace comprising a heatresisting shell, a plurality of pyro-clectrolytic bars within said shell, the protecting heat-resisting rods m, and conducting-supports sustaining the ends of said bars.

2. An electric furnace comprising a heatresisting shell, a plurality of pyro-eleetrolytic bars within said shell, conducting-supports arranged in parallel circuits sustaining the ends of said bars, and means of supplying electrical currents to said supports.

3. An electric furnace comprising a heatresisting shell, a plurality of pyro-electrolytic bars within said shell, conducting-summits sustaining the ends of said bars, means of electrically connecting said supports in parallel with a source of electrical currents and resistance-wires in said parallel circuits.

4:. An electric furnace comprising a heatresisting shell, a plurality of pyro-electrolytic bars within said shell, conducting-supports sustaining the ends of said bars, means of electrically connecting said supports in parallel circuits with a source of electrical currents, resistance-wires in said parallel circuits, and a variable rheostat in the lead-wire to said parallel circuits.

5. In an electric furnace having a plurality of pyro-electrolytic bars within a heat-resisting shell, means of protecting the substance to be heated and the said bars during the insertion and withdrawal of said substance, consisting of the heat-resisting rods m, arranged in parallel with said bars, between said bars and the space occupied by said substance.

In testimony whereof I have hereunto set my hand in the presence of two witnesses.

ROMAIN E WV. MYERS;

Witnesses:

EDWARD A. HoLMAN, THOS. J. THOMPSON. 

